linux-kernel - Re: [PATCH v10 049/108] KVM: x86/tdp_mmu: Support TDX private mapping for TDP MMU

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Message-ID: <20221117193127.GN2350331@ls.amr.corp.intel.com>
Date:   Thu, 17 Nov 2022 11:31:27 -0800
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     "Huang, Kai" <kai.huang@...el.com>
Cc:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "Aktas, Erdem" <erdemaktas@...gle.com>,
        "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
        "dmatlack@...gle.com" <dmatlack@...gle.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>
Subject: Re: [PATCH v10 049/108] KVM: x86/tdp_mmu: Support TDX private
 mapping for TDP MMU

On Wed, Nov 16, 2022 at 11:58:46AM +0000,
"Huang, Kai" <kai.huang@...el.com> wrote:

> 
> >  
> > +static inline int kvm_alloc_private_spt_for_split(struct kvm_mmu_page *sp, gfp_t gfp)
> > +{
> > +	gfp &= ~__GFP_ZERO;
> > +	sp->private_spt = (void *)__get_free_page(gfp);
> > +	if (!sp->private_spt)
> > +		return -ENOMEM;
> > +	return 0;
> > +}
> > +
> > 
> [...]
> 
> > @@ -1238,6 +1408,12 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> >  		    is_large_pte(iter.old_spte)) {
> >  			if (tdp_mmu_zap_spte_atomic(vcpu->kvm, &iter))
> >  				break;
> > +			/*
> > +			 * TODO: large page support.
> > +			 * Doesn't support large page for TDX now
> > +			 */
> > +			KVM_BUG_ON(is_private_sptep(iter.sptep), vcpu->kvm);
> > +
> >  
> 
> So large page is not supported for private page, ...
> 
> >  			/*
> >  			 * The iter must explicitly re-read the spte here
> > @@ -1480,6 +1656,12 @@ static struct kvm_mmu_page *__tdp_mmu_alloc_sp_for_split(gfp_t gfp, union kvm_mm
> >  
> >  	sp->role = role;
> >  	sp->spt = (void *)__get_free_page(gfp);
> > +	if (kvm_mmu_page_role_is_private(role)) {
> > +		if (kvm_alloc_private_spt_for_split(sp, gfp)) {
> > +			free_page((unsigned long)sp->spt);
> > +			sp->spt = NULL;
> > +		}
> > +	}
> 
> ... then I don't think eager splitting could happen for private mapping?
>  
> If so, should we just KVM_BUG_ON() if role is private?

Right, will remove this part from this patch series and move it to large page
support series.
-- 
Isaku Yamahata <isaku.yamahata@...il.com>